Terahertz Multiple Vortex Beams Generation Based On Graphene Metasurface

This paper investigates the generation of vortex beams using a graphene metasurface at terahertz frequency band. A design of $20 \times 20$ unit-cell elements is described at 1.2THz. Each element is a graphene ring patch printed on silicon dioxide grounded substrate of $75 \times 75 \times 25 \mu \mathrm{m}^{3}$. The plane-wave excitation is investigated. The graphene reconfigurable surface conductivity is used to control the beam shape, direction, and directivity radiated from the metasurface, through the application of DC biasing voltages. A depiction of a single vortex beam in various orientations $\theta=0,30^{\circ}, 50^{\circ}$, and $70^{\circ}, \varphi=90^{\circ}$ for mode $l=1$ is presented. The graphene metasurface possesses the capability to convert linearly polarized input into multiple beams exhibiting orthogonal modes. The capacity of wireless communication in the terahertz band can be enhanced by utilizing the graphene metasurface.